E-mail server device and certificate management method of the e-mail server device

Abstract

An e-mail server device includes a certificate storage unit, an SMTP reception unit, a signature unit, an SMTP transmission unit, a validity determination unit and an update request e-mail generating unit. The certificate storage unit stores a certificate for each account. The SMTP reception unit receives e-mail. The signature unit assigns a digital signature to the e-mail received by the SMTP reception unit by using a certificate of an account of a transmitter. The SMTP transmission unit transfers the e-mail assigned with the digital signature. The validity determination unit determines whether or not the certificate stored in the certificate storage unit is necessary to be updated. When the validity determination unit determines that the certificate is necessary to be updated, the update request e-mail generating unit transmits update request e-mail to the account for requesting an update of the certificate.

1 . An e-mail server device, comprising: 
 a certificate storage unit which stores a certificate for each account;    a reception unit which receives e-mail;    a digital signature unit which assigns a digital signature to the e-mail received by the reception unit by using the certificate of an account of a transmitter;    a transfer unit which transfers the e-mail assigned with the digital signature;    a determination unit which determines whether or not to update the certificate stored in the certificate storage unit; and    an update requesting unit which transmits an update request e-mail to the account for requesting an update of the certificate when the determination unit determines that the update of the certificate is necessary.    
   
   
       2 . The e-mail server device according to  claim 1 , wherein the determination unit determines whether or not to update the certificate according to whether the certificate stored in the certificate storage unit is valid or invalid.  
   
   
       3 . The e-mail server device according to  claim 2 , wherein the determination unit determines whether the certificate is valid or invalid in accordance with an expiration date of the certificate.  
   
   
       4 . The e-mail server device according to  claim 2 , wherein the determination unit determines whether the certificate is valid or invalid in accordance with a presence or an absence of a lapse of the certificate.  
   
   
       5 . The e-mail server device according to  claim 1 , wherein the determination unit determines whether or not to update the certificate according to whether a remaining length of an effective period of the certificate stored in the certificate storage unit is a prescribed length or shorter.  
   
   
       6 . The e-mail server device according to  claim 5 , wherein the determination unit determines whether or not the remaining length of the effective period of the certificate is the prescribed length or shorter in accordance with the expiration date of the certificate.  
   
   
       7 . The e-mail server device according to  claim 1 , further comprising: 
 an update accepting unit which accepts an update instruction of the certificate by e-mail; and    an updating unit which updates the certificate stored in the certificate storage unit when the update accepting unit accepts the update instruction.    
   
   
       8 . The e-mail server device according to  claim 7 , further comprising an update notification unit which transmits an update notification e-mail to the account for notifying that the updating unit has updated the certificate.  
   
   
       9 . The e-mail server device according to  claim 1 , wherein the determination unit periodically determines whether or not to update the certificate.  
   
   
       10 . The e-mail server device according to  claim 1 , wherein the determination unit determines whether or not to update the certificate when the reception unit receives the e-mail.  
   
   
       11 . A certificate management method of an e-mail server device, comprising the steps of: 
 storing a certificate for each account;    receiving e-mail;    assigning a digital signature to the e-mail received at the receiving step by using the certificate of an account of a transmitter;    transferring the e-mail assigned with the digital signature;    determining whether or not to update the certificate stored at the storing step; and    requesting an update of the certificate by transmitting an update request e-mail to the account when a determination is made at the determining step that the certificate is necessary to be updated.    
   
   
       12 . The certificate management method of the e-mail server device according to  claim 11 , wherein at the determining step, a determination is carried out as to whether or not to update the certificate stored at the storing step according to whether the certificate is valid or invalid.  
   
   
       13 . The certificate management method of the e-mail server device according to  claim 12 , wherein at the determining step, a determination is carried out as to whether the certificate is valid or invalid in accordance with an expiration date of the certificate.  
   
   
       14 . The certificate management method of the e-mail server device according to  claim 12 , wherein at the determining step, a determination is carried out as to whether the certificate is valid or invalid in accordance with a presence or an absence of a lapse of the certificate.  
   
   
       15 . The certificate management method of the e-mail server device according to  claim 11 , wherein at the determining step, a determination is carried out as to whether or not to update the certificate stored at the storing step according to whether or not a remaining length of an effective period of the certificate is a prescribed length or shorter.  
   
   
       16 . The certificate management method of the e-mail server device according to  claim 15 , wherein at the determining step, a determination is carried out as to whether or not the remaining length of the effective period of the certificate is the prescribed length or shorter in accordance with an expiration date of the certificate.  
   
   
       17 . The certificate management method of the e-mail server device according to  claim 11 , further comprising the steps of: 
 accepting an update instruction of the certificate by e-mail; and    updating the certificate stored at the storing step when accepting the update instruction at the accepting step.    
   
   
       18 . The certificate management method of the e-mail server device according to  claim 17 , further comprising the step of notifying that the certificate has been updated at the updating step by transmitting update notification e-mail to the account.  
   
   
       19 . The certificate management method of the e-mail server device according to  claim 11 , wherein at the determining step, the determination as to whether or not to update the certificate is carried out periodically.  
   
   
       20 . The certificate management method of the e-mail server device according to  claim 11 , wherein at the determining step, the determination as to whether or not to update the certificate is carried out when receiving the e-mail at the receiving step.